The present invention relates to a running resistance control apparatus for a chassis dynamometer.
Generally, a chassis dynamometer is arranged to execute a drive simulation of a test vehicle so as to measure various characteristics such as exhaust gas characteristic and fuel consumption. Such a simulation is executed in a manner such as to set the test vehicle on the chassis dynamometer and to drive the test vehicle under a predetermined road running pattern while executing a running resistance control. In order to adapt the chassis dynamometer to various vehicles having various weights, the conventional chassis dynamometer employs an electric inertial control which electrically simulates various weights of test vehicles.
As shown in FIG. 2, a conventional chassis dynamometer comprises a roller 1 which is rotatably supported to a base and on which driving wheels of a test vehicle 2 are set. A dynamometer 3 is interconnected with the roller 1 and is arranged to absorb a rotational power of the roller 1 rotated by the driving of the test vehicle 2. A load cell 4 detects an absorption torque of the dynamometer 3. A scale-up section 5 scales up an output of the load cell 4 from a millivolt (mV) unit to a volt (V) unit. A pulse pickup 6 detects a rotation speed of the dynamometer 3 which speed corresponds to a vehicle speed of the test vehicle 2. An output pulse indicative of the vehicle speed 2 is outputted from the pulse pickup 6 to a frequency modulating section 7 (frequency modulator) where the output pulse is converted into a corresponding voltage value.
A running resistance setting section 8 connected to the frequency modulating section 7 outputs a running resistance torque RRL corresponding to the input voltage on the basis of a predetermined relationship between the vehicle speed and a running resistance torque. A mechanical-loss setting section 9 receives the vehicle-speed indicative voltage and outputs a mechanical-loss torque FMLcorresponding to the vehicle speed on the basis of the predetermined relationship between the vehicle speed and the mechanical-loss torque. An electric inertia setting section 10 is constituted by a differential calculating section 11 and an electric inertia calculating section 12. The differential calculating section 11 obtains an acceleration speed dv/dt of the vehicle 2 by differentiating the output of the frequency modulating section 7. The electric inertia calculating section 12 calculates an electric inertia torque FE=(Wcarxe2x88x92Wo)dv/dt from an output of an inertia setting section 13 for setting an weight Wcar of the vehicle 2 and the output of the differential calculating section 11 wherein Wo is a mechanical inertia of the roller 1 and the dynamometer 3 which is previously stored.
An adding and subtracting section 14 adds the electric inertia torque FE to the running resistance torque FRL and subtracts the mechanical loss torque TML from the sum of the electric inertia torque FE and the running resistance torque FRL. A difference detecting section 15 detects a difference between a torque command value which is an output of the adding and subtracting section 14 and a detection torque which is an output of the scale-up section 5. A torque control section 16 is constituted by an amplifying section 17 for amplifying the output of the difference detecting section 15, a phase control section 18 for outputting a phase control signal according to the output of the amplifying section 17 and a rectifier 19 which is turned on and off according to the phase control signal. The torque control section 16 controls an AC electric source by means of the Lenard control or inverter control and supplies the controlled voltage to the dynamometer 3.
FIG. 3 shows a conventional running resistance control apparatus wherein the running resistance setting section 8 sets the running resistance torque FRL according to the detected vehicle speed V of the test vehicle 2 and outputs it. The mechanical loss setting section 9 sets the mechanical loss FML according to the detected vehicle speed V and outputs it. The differential calculating section 11 obtains the acceleration speed of the vehicle 2 by differentiating the detected vehicle speed V. The electric inertia calculating section 12 calculates the electric inertia torque FE from the output of the differential calculating section 11, the vehicle weight Wcar and the mechanical inertia Wo of the roller 1 and the dynamometer 3 by using the equation FE=(Wcarxe2x88x92Wo)dv/dt. The adding and subtracting section 14 adds the running resistance torque FRLand the electric inertia torque FE and subtracts the mechanical loss torque FML therefrom. The output of the adding and subtracting section 14 is inputted to a dynamometer torque control section 20. The dynamometer torque control section 20 obtains the dynamometer control torque FLC and inputs it to an adding and subtracting section 24. A chassis dynamometer 21 comprises a roller 1 and the dynamometer 3 and is represented by a fixed inertia section 22 constituted by an integral element of the mechanical inertia Wo and a mechanical loss section 23 and the adding and subtracting section 24. The adding and subtracting section 24 subtracts the dynamometer control torque FLC and the output of the mechanical loss section 23 from a drive torque Fcar corresponding to the vehicle weight Wcar.
However, the conventional running resistance control apparatus of a chassis dynamometer produces a control delay time of about 100 milliseconds during the electric inertia control. Therefore, the detected vehicle speed V generates a control error with respect to a target vehicle speed VR obtained under an ideal running condition of the vehicle 2. As shown in FIG. 4, a continuous line shows a target vehicle speed VR which is obtained in case that the vehicle 2 ideally runs receiving the set running resistance. A dotted line shows the detected vehicle speed V affected by the delay of the electric inertia control. The relationship between the target vehicle speed VR and the detected vehicle speed V shown in FIG. 4 is established when the set vehicle weight Wcar is greater than the fixed inertia. When the set vehicle weight Wcar is smaller than the fixed inertia, the acceleration and the deceleration of the vehicle speed inversely function as compared with the case that the set vehicle weight is greater than the fixed inertia. Due to the delay of the electric inertia control, the detection vehicle speed V during the acceleration and the deceleration generates the error with respect to the target vehicle speed. This error badly affects the result of the exhaust gas performance and the fuel consumption as compared with those in case that the vehicle 2 actually runs on a road.
It is an object of the present invention to provide an improved running resistance control apparatus of a chassis dynamometer which apparatus improves the responsibility of an electric inertia control and corresponds a vehicle speed during acceleration and deceleration to a target vehicle speed so as not to affect the fuel consumption and exhaust gas performance.
A running resistance control apparatus according to the present invention is for a chassis dynamometer which comprises a roller on which a test vehicle is set and a dynamometer connected to the roller. The running resistance control apparatus comprises a running resistance setting section which sets a running resistance torque of the test vehicle according to the detected vehicle speed of the test vehicle. A mechanical loss setting section sets a mechanical loss torque according to the detected vehicle speed of the test vehicle. A differential calculating section differentiates the detected vehicle speed of the test vehicle. An electric inertia calculating section calculates an electric inertia torque from the output of the differential calculating section, a weight of the test vehicle and a preset mechanical inertia of the roller and the dynamometer. A target vehicle speed calculating section calculates a target vehicle speed from the detected vehicle speed, a control torque of the dynamometer, the running resistance torque and the mechanical loss torque. A speed amplifying section amplifies a difference between an output of the target vehicle speed calculating section and the detected vehicle speed. A subtracting section subtracts an output of the speed amplifying section from an output of the electric inertia calculating section. An adding and subtracting section adds the output of the running resistance setting section and the output of the subtracting section and subtracts the output of the mechanical loss setting section therefrom. A torque control section controls the control torque of the dynamometer according to the output of the adding and subtracting section.